C. Dincer, E. Laubender, J. Heinze, G. Urban

Cooperation:
Fraunhofer Institute for Applied Solid State Physics, IAF
Univ. Stuttgart, 3. Institute for Physics
Univ. Ulm, IABC
Project Management: State Foundation


Research Objectives:
* Characterisation of diamond coated micro- and nano-electrodes.
* Evaluation of sensitivity and applicability of different electro-analytical methods.
* Application of Scanning Electrochemical Microscope (SECM) to screen membrane pores.

Ultramicroelectrodes and nanodes for electrochemical researches have already been developed and applied at Freiburg Material Research Center and IMTEK. In this connection, the application possibility of such probes ranges from characterisation of simple electrode processes to research in materials science and biosensors [1,3,7,8].

Fig. 1: Diamond electrodes array

In connection with SECM, a method which is further developed and operated in Freiburg [2], surface structure and processes (contactless) can not only be analysed with high spatial resolution, but also electrochemical changes can be performed on the surfaces. Neurotransmitter measurement on a planar three electrodes-microelectrode array was performed for the first time [3]. For the analysis of many electrochemical processes multifiber ultramicroelectrodes were developed, with up to 7 independent measuring sites detecting pH-changes or redox-active molecules simultaneously [4]. These technological possibilities were utilised in the increasing scope for the questions of life sciences. Additionally spatial-resolved proton fluxes on membranes were measured [5] and the ATP-syntheses on the proton-driven H+-ATP synthase were studied by means of SECM-induced pH-changes [6]. Using microminiaturised multi-electrode arrays, also biosensors for monitoring metabolic parameters were produced [7,8].  
 

Fig. 2: Large-scale feedback scan with the SECM vs. ESEM-Image of boron-doped diamond UMEA
 

Experiments on boron-doped diamond ultramicroelectrodes (UME) and UME-arrays (produced by IAF) using SECM show electrochemical inhomogeneities and do not exhibit homogenous surface for the charge transfer and show locally different charge transfer resistance. Therefore, these phenomenon must be particularly noted by the construction of electrodes in submicrometer range.
 

Fig 3: SECM measurement of 2 diamond UMEAs. Comparison between “Constant potential feedback mode” and “Matrix-mode with chronoamperometry”

Due to the larger surface of such layers, also a higher sensitivity is expected. The future works will content the characterisation, selection and optimisation of diamond electrode arrays using standard redox-systems.

References

[1] Jürgen Heinze, Angewandte Chemie 1993, 105, 1327.
[2] J. Ufheil, C. Hess, K. Borgwarth, J. Heinze, Physical Chemistry Chemical Physics 2005, 7, 3185.
[3] C. Pifl, A. Jachimowicz, G. Urban, F. Kohl, P. Goiser, J. Theiner, G. Nauer, Sensors and Actuators B, Vol. 1,1990, 468-472.
[4] N. Baltes, L. Thouin, C. Amatore, J. Heinze, Angewandte Chemie International Edition 2004, 43, 1431.
[5] F. M. Boldt, J. Heinze, M. Diez, J. Petersen, M. Borsch, Analytical Chemistry 2004, 76, 3473.
[6] N. Baltes, J. Heinze, Chemphyschem 2009, 10, 174.
[7] I. Moser, G. Jobst and G. A. Urban, Biosensors and Bioelectronics, Vol. 17, 2002, 297-302.
[8] E. Laubender, F. Garay, J. Heinze, G. Urban, TRANSDUCERS 2009. International Solid-State Sensors, Actuators and Microsystems Conference, 2009, 21, pp. 140.